Function inside for loop not working

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Peter Hinderberger 2020-11-5

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https://ww2.mathworks.cn/matlabcentral/answers/637520-function-inside-for-loop-not-working

评论： Steve Eddins 2020-11-6

Hi,

I am trying to iterate the diagonal filling of a previously defined, 0 valued hypercube object with a for loop of the following form:

EDIT - REMAINING CODE:

% Load and adjust test image, convert to .png (probably unnecessary)

addpath('D:\Users\Peter\Desktop\Masterarbeit\Messdaten\Bilder_Einfach');

img = imread('BspBild_1.jpg');

imwrite(img, 'BspBild.png');

img = double(rgb2gray(imread('BspBild.png')));

img = rescale(img);

sz = size(img);

% Create empty hypercube

zerocube = zeros(detformat_y, 2*detformat_x, n_lambda);

hcube = hypercube(zerocube, wavelengths);

% Add image to the first band

hcube = assignData(hcube, 1:411, detformat_x/2+1:640+detformat_x/2, 1, img);

% Show image as first hypercube band (for testing reasons)

figure(2)

imshow(hcube.DataCube(:, :, 1))

title('Cube-Ausschnitt')

% loop to "shear" image in the wavelength direction EDIT - END

for k = 1:n_lambda % n_lambda is the number of bands

temp = img(:, k); % img is the monochromatic image that should fill a diagonal line

hcube = assignData(hcube, :, k, k, temp);

end

the function assignData is defined in the Image Processing Toolbox Hyperspectral Imaging Library and works fine outside the for loop.

Whenever I try to execute the code it gives me "Unrecognized function or variable 'assignData'." in the line with this function.

Since directly indexing inside the hcube.DataCube object is not possible this function seems to be the only option to change hyperspectral data.

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Geoff Hayes 2020-11-5

Peter - can you show more of your code? It isn't clear why calling this function within the loop would fail whereas calling it outside the loop would succeed.

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Answer 1

Steve Eddins 2020-11-5

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/637520-function-inside-for-loop-not-working#answer_535415

One possible explanation for the observed behavior is that the variable hcube does not actually contain a hypercube object when the call to assignData happens inside your for-loop. Since we don't see the code before the for-loop, I can't really guess at why that might be. I recommend that you use the debugger and single-step through your code, making sure that the variables contain what you think they should contain at each step.

Also, does your real code include the single quotes around the colon character in the call to assignData? I don't this code will work as it is written here, without the single quotes.

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Peter Hinderberger 2020-11-6

编辑：Peter Hinderberger 2020-11-6

The line to test if there is image data in the hcube.DataCube object works fine, and i can also view it in the hyperspectral viewer.

You're right - there should be quotes around the character data according to the help center. It didn't show this error again, just takes eternally long. But why do i need those quotes here? They are not needed when i index into it via "x:y" as in a normal array, but they are if i only use ":" ?

This for loop takes far too long, but i don't know how to do it faster. Has somebody an idea?

I have to do this for many images to create the object to work with, but waiting for hours will probably be a problem.

In any case thanks a lot, i somehow knew that it has to be such a small thing, but i wouldn't have expected to need those thingies when indexing :)

Steve Eddins 2020-11-6